The present invention relates to a control device with an electric servo motor, by means of which a throttle device can be arranged to open to a greater or lesser degree, the passage diameter of a flow line, especially the passage diameter of a by-pass line around a throttle valve disposed in the intake line of an internal combustion engine. Such control elements are already known (German Offenlegungsschrift Nos. 28 12 292, 30 01 473, 30 19 167), which, however, have the disadvantage that in case of a loss of the current supply of the servo motor or, during their use in a motor vehicle, when the internal combustion engine is turned off, the throttle device controlling the diameter of the flow line remains in that opening position into which it was placed by the servo motor at that time, or is moved to a fully closed or fully open position, which can cause problems during starting or further running of the internal combustion engine.